Presently, nearly 500 million tons of fly ash are produced annually in the world, with a global recycling rate of only 15 %. The problem associated with fly ash lies in the fact that its disposal requires large quantities of land and water. At present, resource recovery from coal fly ash is one of the most important issues in waste management. In another area of research, microporous (zeolite 4A) and mesoporous (MCM-41) materials have found a number of important applications such as adsorption and separation, ion exchange, catalysis and molecular hosts. Therefore, converting coal fly ash into microporous (zeolite 4A) and mesoporous (MCM-41) materials not only eliminates/relieves the disposal problem of coal fly ash but also turns a waste material into a useful one....[ Read more ]

Presently, nearly 500 million tons of fly ash are produced annually in the world, with a global recycling rate of only 15 %. The problem associated with fly ash lies in the fact that its disposal requires large quantities of land and water. At present, resource recovery from coal fly ash is one of the most important issues in waste management. In another area of research, microporous (zeolite 4A) and mesoporous (MCM-41) materials have found a number of important applications such as adsorption and separation, ion exchange, catalysis and molecular hosts. Therefore, converting coal fly ash into microporous (zeolite 4A) and mesoporous (MCM-41) materials not only eliminates/relieves the disposal problem of coal fly ash but also turns a waste material into a useful one.

The objective of this research is to synthesize pure form (without residual fly ash), single phase and high crystalline zeolite 4A and MCM-41 from coal fly ash. Moreover, the treated coal fly ashes (residual) are also converted into low grade adsorbent for the removal of heavy metal ions in waste water.

The present study indicates that step-change of synthesis temperature during hydrothermal treatment plays an important role in reducing the overall synthesis time, but still maintains a high degree of crystallinity of the samples. In addition, smaller particle size crystals with a narrower particle size distribution can be achieved.

From the performance tests, it shows that the synthesized zeolite 4A samples (from coal fly ash), behaving similar to the commercial one, could be used as detergent builders in laundry as they have a very high calcium binding capacity. Moreover, it can also be concluded that coal fly ash based adsorbents (zeolite 4A, treated coal fly ashes) may be an alternative to more costly adsorbents such as activated carbon and commercial zeolites for the treatment of aqueous wastes containing mixed metal ions.

A green and economic synthesis method for preparing MCM-41 materials from coal fly ash was also reported. The proposed method can offer a convenient way for preparing MCM-41 materials of different pore sizes by controlling the initial synthesis pH. The results demonstrate a possibility of production of MCM-41 materials from coal fly ash on an industrial scale.